It’s not that there haven’t been close calls before: “Cars,” “Cars 2,” “Monsters University.” But in the 20 years since Pixar released “Toy Story,” the animation studio has never released an outright mediocre feature. That unbeaten streak has been broken. Five months after the astounding achievement of “Inside Out” there arrives “The Good Dinosaur.”

A very middling movie, it does have a nifty premise. That asteroid or comet or whatever which hit Earth 65 million years ago and led to the dinosaurs’ extinction? It missed. So this really is
a Jurassic world. The big guys rule the planet. Humans are rarely seen “critters,” annoying presences on the order of bugs or rodents. The dinosaurs are like a nicer, less organized version of the simians in “Planet of the Apes.” Well, most are nicer. Watch out for pterodactyls, especially the one voiced by Steve Zahn, channeling his not-so-inner Dennis Hopper.

These dinosaurs have evolved. They speak English. In the case of a T. rex quite wonderfully voiced by Sam Elliott, they growl English. The fact that they can survive snow and immersion in mountain rivers indicates that they’re no longer cold-blooded. If they’re apatosauruses, they farm corn. No need for plows with such impressive snouts! They also raise chickens. This is an important point, since the tip-off that young Arlo (Raymond Ochoa) is a scaredy-cat — scaredy-dino? — is how much fowl spook him. So does pretty much everything. It will come as no surprise that “The Good Dinosaur” will provide Arlo with multiple opportunities to confront his fears and prove himself to his parents (Jeffrey Wright and Frances McDormand).

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Arlo has to deal with another initially fearsome creature, a young human (Jack Bright). For reasons unexplained, he wears a leafy breechclout. Shades of Ariel’s brassiere in “The Little Mermaid.” Dinosaurs may have evolved, but not dress codes.

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Arlo’s new nemesis is as much canine as hominid. He bounces around on all fours, sniffs the air like a hound, and behaves in a relentlessly endearing manner of the woof-woof sort. Arlo, no fool, dubs him Spot. The name is representative of the imaginative level at which “The Good Dinosaur” generally operates.

The movie’s visuals are gloriously Pixar. The apatosauruses’ farm nestles in a valley of what looks like the high Sierra. The setting is stunning, and the detail with which it’s rendered even more so. Alas, the emotional shamelessness and mechanical plotting are glumly Disney. Also very Disney is having nature do the work of feeling, and feeling (such as it is) do the work of thought. This is definitely the first Pixar movie that seems more like a Disney movie.

“The Good Dinosaur” marks the feature debut for director Peter Sohn. His one previous effort was the Pixar short “Partly Cloudy.” The accompanying short here, directed by Sanjay Patel, is “Sanjay’s Super Team.” An American boy of South Asian heritage conflates Hinduism with super heroics. This comes across as both sweet and hectic. It’s not the best combination.

Sohn’s freshman status may account for the film’s unnerving shifts of tone. “The Good Dinosaur” generally features a sort of sentimentality and emotional reductiveness that make it seem meant for small children as no previous Pixar movie has. The surprisingly crude Dino the Dinosaur look of the apatosauruses contributes to this sense. Yet there’s also the broad comedy of a sequence with T. rexes herding buffalo — yup, just like a western — or one in which Arlo and Spot get high on fermented berries for a sort of “Big Lebowski” moment. Most jarring of all are frequent scenes of nature-red-in-tooth-and-claw violence. Part of the movie would likely make anyone under 10 squirm with boredom. These other parts would make children under 10 (and many adults, too) squirm for a very different reason.